This application is related to simultaneously filed applications xe2x80x9cInjection of encapsulating material on an optocomponentxe2x80x9d and xe2x80x9cOptocomponent capsule having an optical interfacexe2x80x9d.
The present invention relates to a leadframe intended and adapted for encapsulation of optocomponents with a plastics material and a method of encapsulating optocomponents with a plastics material, during simultaneous obtainment of optical interfaces in the capsule wall.
In the earlier patent application SE 9400907-3, filed Mar. 18 1994, a method of encapsulating optocomponents by means of transfer moulding and of obtaining at the same time an optical interface in the wall of the capsule is described. This method is developed from the conventional encapsulating method for microelectronic circuits, where an electrically conducting leadframe is used for establishing an electric connection to microelectronic circuit chips. The leadframe usually consists of a punched or etched metal piece, e.g. of a thin copper or aluminium sheet. The leadframe comprises a special, suitably adapted portion termed xe2x80x9cflagxe2x80x9d, onto which a microelectronic circuit is mounted before being moulded into the encapsulating material. Before the moulding embedment, the microcircuit chip is also electrically connected by friction welding, xe2x80x9cbondingxe2x80x9d, by means of xe2x80x9cbondingxe2x80x9d wires to fingers and thereby also to legs of the leadframe.
Moreover, in encapsulation of optocomponents an optical interface is to be formed in the wall of the capsule having a high accuracy as to the position of the component in relation to another optocomponent or an optical connector device, to which the encapsulated component is to be connected. The required mechanical accuracy is achieved by mounting one or more optocomponents on a common carrier or substrate in the shape of a plate, which thereafter is attached to the flag. Finally the carrier is positioned in relation to the external geometry. For an optical interface, which is compatible with an optical multi-fiber contact of MT-device type, this is achieved by means of V-grooves on the carrier plate, in which guide pins extending through the mould cavity fit. These guide pins are pulled out after the encapsulation and then leave circular cylindrical holes in the encapsulation material. Into these holes, loose cylindrical guide pins are then inserted, at connection of the encapsulated optocomponent to a component having a similar interface.
The published European patent application EP-A1 0 452 634 discloses a leadframe intended for encapsulation of optical modules with a plastics material having several waveguides. In FIGS. 4-7 leadframes having flags intended for electronic circuit elements are shown, where portions of bridges between flag portions and a frame part extending at the edge are zigzag shaped in order to accommodate mechanical strains, which are caused by the plastics encapsulation. The zigzag shaped portions are located outside of the area the leadframe, which is contained inside the encapsulated module and which is shown by the dashed line P.
The published European patent application EP-A1 0 552 419 describes apparatus and a method for manufacturing optical modules by plastics encapsulation of amongst others optocomponents connected to a lead frame. In FIG. 6c it is shown how an optocomponent, using a wire W, is influenced by a pressing force for the purpose of obtaining an exact positioning.
Leadframes for semiconductor capsules are e.g. disclosed in U.S. Pat. Nos. US-A 4,870,474 and 5,150,193 and in the published European patent application EP-A1 0 443 508. Optical components having leadframes are also discribed in U.S. Pat. No. 3,914,786 and the published European patent application EP-A2 0 446 410.
It is an object of the invention to provide a lead frame for mounting a carrier having one or more optocomponents next to a side wall of a capsule.
It is a further object of the invention to provide a leadframe for electrical connection of a carrier having one or more optocomponents, which leadframe allows that the carrier can be oriented for an accurate positioning during the moulding embedment of the carrier.
It is a further object of the invention to provide an encapsulated optical component and a manufacturing process thereof, in which a carrier attached to a leadframe becomes accurately positioned during the encapsulation process.
These and other advantageous objects are achieved by the invention and appear from description hereinafter, the scope of the invention being defined in and the characteristics thereof being set out in the appended claims.
A leadframe is designed, so that:
I) a flag, to which the very main portion of the optocomponent is attached, is placed asymmetrically next to the mould cavity wall, so that an optical interface is obtained in the capsule wall,
II) the flag is flexibly attached in the leadframe for the purposes of:
a) obtaining an adjustment possibility of the flag in relation to the rest of the leadframe,
b) obtaining an adjusted pressure force on the flag, and thereby on the optocomponent, in relation the mould cavity wall in order to minimize after-treatment of the optical interface,
c) obtaining an adjusted pressure force on the flag, and thereby on the optocomponent, so that an exact positioning of the optocomponent can be obtained. Bridges by means of which the flag is attached to the leadframe have for this purpose a zigzag shape.
Hence, a leadframe having a flag, to which very main part of the optocomponent is attached, is thus used for the electrical connection in encapsulation of an optocomponent. The leadframe also comprises connection portions for electrical connection to both the optocomponent and to the exterior, to adjacent electrical circuits. The flag is asymmetrically placed at the outer edge of the leadframe, centrally on this outer edge, and will then be placed next to a wall in a mould cavity in a mould during the encapsulating process. Hereby, an optical interface of standard type having guide pins can be obtained in the capsule wall. The flag is attached somewhat movably by means of zigzag shaped bridges to the other portions of the leadframe in order to enable the flag and hereby the optocomponent to be moved somewhat in relation to the rest of the leadframe. For a suitable width and shape of the zigzag shaped bridge portions an adjusted elastic return force on the flag and thereby an the optocomponent is also obtained, so that it can be pressed against and firmly be retained against positioning means, in the shape of for instance guide pins, which shall be located in guide grooves of the optocomponent during the moulding operation.
A leadframe of an electrically conducting material for connection of electrical connections on an optocomponent generally comprises a flag in the shape of a usually rectangular field for attachment to a main part of the optocomponent, further it comprises connection fingers, the ends of which are intended to be electrically connected, in particular through bonding, to terminals on the optocomponent, and support parts, which extend between the connection fingers and connect to these at areas at a distance from the ends of the connection fingers, which are intended for connection to the component. Further, there are support bridges, which connect the flag to the support parts and which are located in such a place, that the support bridges connect to the support parts at an end thereof. Moreover, the flag shall be located at a side of the frame in order that an optocomponent attached to the flag and an edge thereof shall become positioned at the outer edge of a capsule containing the component.
The support bridges have advantageously the shape of flat bands, which thus are located in one and the same plane and are zigzag shaped, i.e. each of the bands is alternatingly bent to one side and another side, as seen when moving from the connection area of the bridge at a support part to the connection area at the flag, in order to allow an elastic retainment of the flag and in order to give this some movement possibility. The ends of the connection fingers, which are intended for connection to the component, can be placed next to an essentially straight side or a edge of the flag, preferably an edge, which is opposite to the edge of the flag, which during positioning of an optocomponent at an outer side of a capsule, is located next to this outer side. The support parts then advantageously extend essentially perpendicularly to this essentially straight edge of the flag.
An encapsulated optoelectric component obtained together with the leadframe then generally comprises an optocomponent carrier having areas arranged thereon for electrical connection, an optical interface at one side or edge thereof having inlets/outlets for light signals or having waveguide ends, further leadframe parts, which have been obtained from the leadframe for electrical connection of areas on the optocomponent carrier and which comprise outer connection tongues, and moreover an encapsulating enclosure enclosing the main part of the optocomponent carrier and of the leadframe. The leadframe parts also comprise a flag, which is attached to a main part of the optocomponent and which is located at a side or a surface of the component or of its main part, and further the leadframe parts comprise terminal parts, which are electrically connected through wires to terminals on the optocomponent carrier. The leadframe parts in the encapsulated component will according to the above advantageously comprise zigzag shaped parts, that extend from the flag.
In manufacturing such an encapsulated optocomponent the following steps are generally carried out. The optocomponent is first manufactured having guide grooves for guide pins on a first, top surface. Then, it is attached to a flag in a leadframe, guide pins are placed in an opened mould cavity in a mould and the leadframe having an attached optocomponent is placed in the opened mould cavity of the mould, so that the guide pins engage in the guide grooves, where the two latter steps can change positions with each other. Thereupon the mould cavity of the mould is closed and then the arrangement of the leadframe with the optocomponent in relation to guide pins is such that the guide pins and the optocomponent hereby become correctly positioned in relation to each other and the leadframe is retained in the mould cavity, whereby an elastic force originating from the leadframe is applied to the optocomponent, so that this with its guide grooves is pressed onto the guide pins and the optocomponent is accurately guided into its intended position. Finally, the encapsulation material is introduced into the closed mould cavity and is allowed to solidify, the mould cavity is opened, the guide pins can be extracted and the moulded body can be removed from the mould cavity. The elastic force from the leadframe, acting on the flag is suitably obtained, by the fact that the flag is attached to the other part of the leadframe through bridge parts having such a geometric shape, that they can be elastically or resiliently prolonged.